An elevator typically comprises an elevator car and a counterweight, which are vertically movable in a hoistway. These elevator units are typically interconnected by ropes (later referred to as upper ropes) that suspend these elevator units on opposite sides of one or more rope wheels mounted higher than the elevator units. For providing force for moving the suspension ropes, and thereby also for the elevator units, one of the wheels is typically a drive wheel engaging the upper ropes. In addition to the upper ropes, the elevator may need to be interconnected by ropes which hang from the elevator car and the counterweight. This type of ropes (later referred to as lower ropes) are often used to provide compensation for the weight of the hoisting ropes. Particularly, in this way the unbalance, which is caused by the upper ropes in situations where the elevator car is run to its extreme position, can be eliminated. However, these ropes may alternatively or additionally be used to provide so called tie-down function for the elevator. The upper ropes and/or the lower ropes may be belt-like.
A challenge with the solutions of prior art has been to guide the ropes with non-driven rope wheels such that reliable guidance for the ropes in axial direction of the rope wheels is provided. One proposed way of guiding ropes of an elevator is cambered shape of the rope wheel. In prior art, it has been proposed that the ropes can pass around a rope wheel having a cambered shape for each of the ropes. The cambered shape of the rope wheel circumference has a tendency to centralize the belt-shaped rope to pass along the peak of the cambered shape. However, it has been noticed that when using cambered guidance, some unintended behavior is occasionally encountered in some conditions. It has been noticed particularly, that a big part of the unintended behaviour is a result of tension differences between adjacent ropes and between successive parts of individual rope which are on opposite sides of a rope wheel. The tension differences, on the other hand, have been noticed to result meaningfully from variations in location of the rope on the cambered shape. That is, adjacent ropes can momentarily pass at different points of the cambered shape. This kind of variations are illustrated in FIG. 1 of the application. Tension differences may also be caused by rope wheel diameter tolerances and rope dimension tolerances. Due to one or more of these reasons it results that individual ropes are turned with slightly different diameters as compared to each other. As a result, excessive tension can be formed for parts of individual ropes. Because the ropes share the rope wheel, the tension can be released only by sliding of the overtensioned individual ropes along the rope wheel. However, this is unwanted as such due to the increase of rope wear it causes. On the other hand, should the engagement of ropes be very firm, such as based on very high friction, the slipping can be avoided but the downside is that loose rope is formed on the less tensioned parts of the rope. For example, with D530 rope wheel, adjacent ropes are at worst turned with roughly 1.8 mm different diameters, which can mean 0.33% slip over the rope wheel in the long run. If this is combined with high friction coefficient between the rope wheel and the rope, and long travel distances, the ropes are reeved so unequally that rope forces start varying remarkably. This may lead to poor rope life time or even rope damages if loose rope starts touching to other elevator components.